I like to know if a girl reverts to Islam and her parents are against her, how can she marry? Who will be her Wali? Can she marry without a Wali with witness? If there is no Wali then what to do? What is the Islamic solution?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The presence (and consent) of the guardian of a woman is a compulsory condition for the validity of her marriage.

‘Aa’ishah narrated, narrated that the Prophet said: “The marriage of a woman who marries without the consent of her guardian is void.” (He repeated this three times.” [Ahmad, Abu Daawood, At-Tirmithi, and Ibn Maajah with a good chain of narrators]

In the case of lack of her guardian, or the guardian is not able to take her guardianship because he is not Muslim and the woman is Muslim, then the Muslim judge or his deputy would marry her off. The last part of the above Hadeeth is "If there is a dispute, the Sultan (ruler) is the guardian of one who has no guardian.”

For more benefit on a woman’s marriage without guardian, please refer to Fataawa 92758, 85057, 226429, 132754, and 269080.

Also, for more benefit that a non-Muslim man cannot be a Wali (guardian) of a Muslim woman in the marriage contract, please refer to Fataawa 225424, 88488, 86524, and 246439.

Allah knows best.